Pyrometric cones are very important for successful, repeatable firings. But we get many questions about cones and how they work. So here is a summary of almost everything I know about cones

Q. How do cones work?
A. Pyrometric cones are slender pyramids made from about 100 carefully controlled compositions. Each cone number is unique in measuring temperature within a small temperature range (less than 30°C). Cones measure the amount of heat absorbed. As the cone nears its maturing range, it softens and the tip begins to bend, drawn down by the influence of gravity or the weight of the sensing rod for cones used in the Kiln-Sitter. It typically takes about 20 minutes for the cone to bend fully. Each higher cone number requires more heat to bend. Faster heating rates require the cone to be heated to a higher temperature.

Q. When is my cone considered "bent"?
A. Cone bending is measured in degrees. Straight up is 0 degrees. When the tip is completely bent over so that the tip just barely touches the kiln shelf, that is 90 degrees. In general, a cone is considered "bent" when it is at about 90 degrees. But different potters have different thoughts about this. The most important thing is for you to be consistent with your own firings, in order to maintain predictable results. Cones bend faster the further along they are, so watch closely toward the end!

Q. What temperature does a particular Cone correspond to?
A. This is a common question, with no real answer. It depends on the rate of temperature increase. Remember that cones measure total heat over the whole firing. So if you fire quickly, your maximum temperature will have to be hotter than if you fire slowly (to reach the same Cone). The following link contains a chart of temperatures assuming a certain temperature rise. The rate of increase during the last 300 degrees is the most important. In other words, during the first 1500 degrees of firing (Fahrenheit), how fast you fire won't affect the end temperature very much. It is primarily the higher temperatures that will affect the end temperature. See Chart Below

Q. I have an old box of cones. Is it still good?
A. Yes. Cones do not change with age. According to Orton who manufactures the cones: "We have Pyrometric cones over 25 years old that we use for comparison testing and standardization. We do keep improving cones, though. Today?s cones are more uniform and perform better and more consistently than those we made 5, 10, or 50 years ago. Also, some changes occur when the supplier of our raw materials goes out of business.

Q. My cones got wet. Can they still be used?
A. Cones are not normally affected by usual amounts of moisture such as humidity in the air. If the cones are damp it is best to dry them out before use. If the cones have been extremely wet they should not be used. An example of this might be cones that were in a flooded basement or studio. These cones may have retained their shape but they may have lost their strength and can possibly break off in the Kiln-Sitter if they are small cones. The large cones that have been wet may not deform with the proper accuracy.

Q. Why should I use Cones?
A. If you have a manual kiln, the only way to determine accurately when it is time to turn the kiln off is with Cones. If you have a Kiln-Sitter, the Cone will trip the Kiln-Sitter when the Cone bends, turning off the kiln. If you don't have a Kiln-Sitter you will manually watch the Cone through a spy hole or peep hole, and turn the kiln off when the Cone is bent.

If you have an electronic kiln, you don't need Cones. But it is still a very good idea to put Cones in. You can ensure that your kiln temperature is calibrated correctly. By putting Cones on every shelf, you can determine if there are hot and cold spots in the kiln. If the power goes out, you will be able to continue firing if you have Cones in. And finally, if you have any problems with your firing such as glazes not coming out the right color, or bubbling, you will know for sure what temperature was reached in that part of the kiln, which will be useful for troubleshooting. At the very least, with an electronic kiln, you should put Cones in every few firings to make sure the kiln doesn't drift and continues to fire at the right temperature as the elements age.

Q. What Cone number should I use?
A. It is best to use the Cone number your glaze matures at, plus 1 Cone above and 1 Cone below. When the lowest Cone bends, you can start getting ready to turn off the kiln, or start slowing it down (especially with gas kilns). You will be at the right temperature to turn off when the Cone below is very slightly bent, the Cone above is extremely bent over (almost melted looking), and the middle Cone is bent to 90 degrees.

Q. Which type of Cone do I want?
A. - Orton Jr Cones are used in Kiln-Sitters.
- Orton Standard Cones are used in Cone packs. A Cone pack is usually made by taking 3 cones, imbedding them in some clay, and allowing the clay to dry before firing. The 3 Cones include one at the firing temperature called the Firing Cone, 1 above called the Guard Cone and 1 below called the Guide Cone. For example, if you are firing at Cone 6, you use a #5, #6 and #7 Cone.
- Orton Self Supporting Cones are used for placement in the kiln when you aren't using a clay pack. They stand up by themselves.
- The last two are often called "witness cones" because you are "witnessing" or "watching" to see how far they bend.
- It is possible to use Orton Jr Cones as "witness cones" but these cones require slightly higher temperatures to bend, so you won't be as accurate.

Q. How exactly does a Kiln Sitter work?
A. The Kiln Sitter shuts off the kiln when a small cone placed under the sensing rod receives enough heat for it to fully bend. Bending is caused by the weight of the sensing rod. Note that because the cone in the Kiln Sitter is located at the kiln wall (closer to the heating elements), it frequently receives more heat than witness cones, causing the kiln to shut off early. Using the next hotter cone may be necessary. You can use a witness cone (or the 3-cone pack) to determine whether your kiln is shutting off early. Put the witness cones on a shelf near the Kiln Sitter to determine if a difference exists between the shelf and Kiln Sitter cones.

Cone Equivalent Temperatures (F)
	Self Supporting Cones 1 3/4" mounting height						Large Cones				Small 15/16" Height
	Regular			Iron Free			Regular		Iron Free		Regular	PCE
	Heating Rate (F/hour)						Heating Rate (F/hour)
Cone	27	108	270	27	108	270	108	270	108	270	540	270
022	1049	1087	1094				N/A	N/A			1166
021	1076	1112	1143				N/A	N/A			1189
020	1125	1159	1180				N/A	N/A			1231
019	1213	1252	1283				1249	1279			1333
018	1267	1319	1353				1314	1350			1386
017	1301	1360	1405				1357	1402			1443
016	1368	1422	1465				1416	1461			1517
015	1382	1456	1504				1450	1501			1549
014	1395	1485	1540				1485	1537			1598
013	1485	1539	1582				1539	1578			1616
012	1549	1582	1620				1576	1616			1652
011	1575	1607	1641				1603	1638			1679
010	1636	1657	1679	1600	1627	1639	1648	1675	1623	1636	1686
09	1665	1688	1706	1650	1686	1702	1683	1702	1683	1699	1751
08	1692	1728	1753	1695	1735	1755	1728	1749	1733	1751	1801
07	1764	1789	1809	1747	1780	1800	1783	1805	1778	1796	1846
06	1798	1828	1855	1776	1816	1828	1823	1852	1816	1825	1873
05½	1839	1859	1877	1814	1854	1870	1854	1873	1852	1868	1909
05	1870	1888	1911	1855	1899	1915	1886	1915	1890	1911	1944
04	1915	1945	1971	1909	1942	1956	1940	1958	1940	1953	2008
03	1960	1987	2019	1951	1990	1999	1987	2014	1989	1996	2068
02	1972	2016	2052	1983	2021	2039	2014	2048	2016	2035	2098
01	1999	2046	2080	2014	2053	2073	2043	2079	2052	2070	2152
1	2028	2079	2109	2046	2082	2098	2077	2109	2079	2095	2163
2	2034	2088	2127				2088	2124			2174
3	2039	2106	2138	2066	2109	2124	2106	2134	2104	2120	2185
4	2086	2124	2161				2120	2158			2208
5	2118	2167	2205				2163	2201			2230
5½	2133	2197	2237				N/A	N/A			N/A
6	2165	2232	2269				2228	2266			2291
7	2194	2262	2295				2259	2291			2307
8	2212	2280	2320				2277	2316			2372
9	2235	2300	2336				2295	2332			2403
10	2284	2345	2381				2340	2377			2426
11	2322	2361	2399				2359	2394			2437
12	2345	2383	2419				2379	2419			2471	2439
13		2428	2458				2410	2455				2460
13½		2466	2493
14		2489	2523				2530	2491				2548
14½		2527	2568
15		2583	2602				2595	2608				2606
15½		2617	2633
16		2655	2687				2651	2683				2716
17		2694	2709				2691	2705				2754
18		2736	2746				2732	2743				2772
19		2772	2786				2768	2782				2806
20		2811	2824				2808	2820				2847
21		2851	2860				2847	2856				2883
23		2890	2898				2887	2894				2921
26							2892	2921				2950
27							2937	2961				2984
28							2946	2971				2995
29							2955	2993				3018
30							2977	3009				3029
31							3022	3054				3061
31½							3063	3088				3090
32							3103	3123				3123
32½							3124	3146				3135
33							3150	3166				3169
34							3195	3198				3205
35							3243	3243				3245
36							3268	3265				3279
37												3308
38												3362
39												3389
40												3425
41												3578
42												3659